Moern medicine makes regular use of scores and indices that put doctors' memory and calculation skills to the test. The advent of personal computers, the Web, and more recently personal digital assistants (PDA) saw the rise of a class of medical software called medical calculators. Their purpose is to allow easy calculation of various scores and indices, presenting the user with a friendly interface that hides the complexity of the formulas. Most offer helpful information such as result interpretation guides and medical literature references.